1. Field of the Invention
This invention relates to a heat-sensitive recording sheet having an improved writing quality in the use of oily ink.
2. prior Art
In general, a heat-sensitive recording sheet is produced by applying on a support, such as paper, synthetic paper, film, plastic, etc., a coating material which is prepared by individually grinding and dispersing a colorless chromogenic dye and an organic color-developing agent, such as phenolic material, etc., into fine particles, mixing the resultant dispersion with each other and then adding thereto binder, filler, sensitizer, slipping agent and other auxiliaries. The coating, when heated by thermal pen, thermal head, hot stamp, laser beam, etc., undergoes instantaneously a chemical reaction which forms a color. These heat-sensitive recording sheets have now been finding a wide range of applications, including industrial measurement recording instruments, terminal printers of computer, facsimile equipment, automatic ticket vending machines, printer for bar-code-label, and so on. In recent years, as the application of such recording is diversified and the performance of such recording equipment is enhanced, high qualities are required for heat-sensitive recording sheets. For example, even with small heat energy in a high speed recording, both the clear image with a high density and the better preservability such as better resistance to light, weather and oil, etc. are required.
In recent years, heat-sensitive recording papers are widely employed, so that the writing with a felt-pen using oily ink is often made after the recording. In this case, there is a problem in that the original color of oily ink is not obtained, since the original color is mixed with the developed color of a heat-sensitive recording sheet. For example, an oily red color of ink written on a black-color-developing heat-sensitive recording sheet is mixed with the developed black color of the heat-sensitive recording paper, so that the original red color is not obtained It is true for the colors often than a red color.